Sugarcane has been cultivated as a raw material for sugar, liquor, and the like for edible use. In addition, sugarcane has been used as, for example, a raw material for biofuel in a variety of industrial fields. Under such circumstances, there is a need to develop novel sugarcane varieties having desirable characteristics (e.g., sugar content, enhanced vegetative capacity, sprouting capacity, disease resistance, insect resistance, cold resistance, an increase in leaf-blade-length, an increase in leaf area, and increased stalk length). Also, Gramineae plants, including sugarcane, are generally used for starting materials for alcoholic beverages and biofuels.
Hybridization of Gramineae plants, including sugarcane, rice, and maize, has been actively carried out in an attempt to improve existing varieties; i.e., production of new varieties with traits of interest. In general, the following three methods may be used for identification of a plant variety/line: “characteristics comparison” for comparison of characteristics data, “comparison during cultivation” for comparison of plants cultivated under the same conditions, and “DNA assay” for DNA analysis. There are many problems in line identification with characteristics comparison or comparison during cultivation, including low precision due to differences in cultivation conditions and long-term field research that requires a number of steps.
In particular, sugarcane plants are much larger than other crops, and it is accordingly difficult to conduct line identification via field research. Further, production of a novel sugarcane variety necessitates production of tens of thousands of hybrids via crossing, followed by seedling selection and stepwise selection of excellent lines. Eventually, 2 or 3 types of novel varieties having desired characteristics can be obtained. In order to produce a novel sugarcane variety, as described above, it is necessary to cultivate and evaluate an enormous number of lines, to prepare a greenhouse or field, and to undertake highly time-consuming efforts.
Therefore, it has been required to develop a method for identifying a Gramineae plant, and in particular, a sugarcane line, having desired characteristics with the use of markers present in the genome. In particular, upon production of a novel sugarcane variety, if excellent markers could be used to examine a variety of characteristics, the above problems particular to sugarcane would be resolved, and the markers would be able to serve as very effective tools. Since sugarcane plants have a large number of chromosomes (approximately 100 to 130) due to high polyploidy, however, the development of marker technology has been slow. While the USDA reported genotyping concerning sugarcane plants with the use of SSR markers (Non-Patent Document 1), the precision of genotyping is low because of the small numbers of markers and polymorphisms in each marker. In addition, the above genotyping is available only for American/Australian varieties, and therefore, it cannot be used for identification of the major varieties cultivated in Japan, Taiwan, India, or other countries, or lines that serve as useful genetic resources.
In addition, Non-Patent Document 2 suggests the possibility that a sugarcane genetic map can be produced by increasing the number of markers, comparing individual markers in terms of a characteristic relationship, and verifying the results. Non-Patent Document 2, however, does not disclose a sufficient number of markers, and markers linked to desired characteristics have not been found.
An example of marker development is that of an Aphanornyces cochlioides-resistant related marker in sugar beet disclosed in Patent Document 1. Also, Patent Document 2 discloses a technique for selecting a maize variety with the utilization of a marker linked to a trait of interest.
There are wild-type sugarcane species (scientific name: Saccharum spontaneum L.). Examples of known wild-type sugarcane species include Glagah found in Indonesia, Saccharum spontaneum found in Japan, and Kash (Kans Grass) found in the Bengali-speaking regions. Glagah, Saccharum spontaneum, and Kash are general names of wild-type sugarcane species in relevant areas. In order to designate a specific variety or line, according to need, individual systemic names that include information such as names of areas in which samples were obtained or numbers indicating relevant nations are occasionally used. In general, a wild-type sugarcane species is characterized by exuberant growth and high environmental tolerance, it has a stalk that is thin but strong, it is rich in fiber, and it has excellent tolerance against diseases and pests, such as dwarf disease and yellow streak virus. While sugar content is generally low, and it is 1% to 3% or lower in the case of Glagah, sugar content of some wild-type sugarcane species harvested in Japan exceeds 10%. That is, the degree of variation is large.
By means of interspecies crossing or intergeneric crossing with wild-type sugarcane species, excellent properties of wild-type sugarcane species in terms of stalk extension or multiple branching are introduced into sugar-producing varieties or Gramineae plant varieties other than sugarcane. Many interspecies hybrids have been found to be excellent in low-temperature extension and final stalk length through experiments, and the genome of a wild-type sugarcane species is deduced to have a distinct gene that causes increased stalk length. Such properties are not observed in sugar-producing varieties. However, no markers related to various properties of wild-type sugarcane species are known. At present, accordingly, it is necessary to perform laborious and time-consuming procedures as described above, in order to select interspecies or intergeneric hybrids with such properties.